Heretofore, urethane-modified polyisocyanurate foams have been known as heat insulating materials excellent in flame retardancy, heat resistance and low smoking property. In this case, it has been essential to replace CFCs and HCFCs used as a blowing agent because of a problem of depleting the ozone layer, and a production process using water as a blowing agent substitute (i.e. carbon dioxide gas generated when water and a polyisocyanate are reacted acts as a blowing agent) has been studied. In a case where water is used as a blowing agent, in a case of continuous production of e.g. laminate boards or metal sidings, the initial adhesion to a facing material tends to decrease, and thus various improvements have been attempted, but no satisfactory result has been obtained.
Further, with respect to the initial adhesion in production process, there are problems in adhesion at the time of cutting in an extremely short period of time (within 5 minutes after initiation of foaming) and adhesion at the time of cutting and handling of a product in the process (after a relatively long period of time, i.e. within about 30 minutes after initiation of foaming), and particularly a decrease in adhesion after a relatively long period of time has been problematic. For example, Japanese Patent No. 2972523 discloses improvement in initial adhesion by use of a fatty acid phosphate containing no halogen, however, adhesion after a relatively long period of time significantly decreases, such being problematic. Japanese Patent Application 2000-199501 discloses improvement in initial adhesion by use of a compatibilizing agent, however, adhesion after a relatively long period of time significantly decreases similarly in most cases, such being problematic.
A schematic drawing illustrating a change with time of adhesion to a facing material, particularly a flexible facing material, in a case of production of e.g. a laminate board or a metal siding using a urethane-modified polyisocyanurate foam as a core, is shown in FIG. 1. From 1 to 2 minutes after removal from a mold, the adhesion is at least 1 kg/10 cm width (peeling test, the same applies hereinafter), however, after from 30 to 60 minutes, the adhesion reaches the minimum. As time further passes, the final adhesion recovers to at least 1 kg/10 cm width, however, the time when the adhesion reaches the minimum overlaps with a time when a product is handled in many cases, and peeling of a facing material tends to take place, thus leading to difficulty in production. The above tendency is particularly remarkable when the density of the foam is decreased. It is an object of the present invention to provide a urethane-modified polyisocyanurate foam having excellent characteristics such as flame retardancy, heat resistance and low smoking property, and further having improved initial adhesion, particularly adhesion after a relatively long period of time, to a facing material particularly a flexible facing material, which employs water as a blowing agent and which employs no CFCs or HCFCs.